FACTS ABOUT MUSCLES
Thus, to summarise, we could say that scientists have found out the following facts about muscles:
1
There are three types of muscle - skeletal, smooth and cardiac
2
Skeletal muscles are generally voluntary and can be made to contract at will
3
Smooth muscles are involuntary and cannot be controlled by the conscious brain (walls of blood vessels, bladder, and gut etc)
4
Skeletal muscles are subdivided into three types of muscle fibres:
a fast fibres, containing less blood and myoglobin, pale in colour and carrying out sudden and brisk movements. They fatigue easily, b slow fibres, containing dense blood vessels, mitochondria and ample myoglobin, red in colour and carrying out slow and prolonged movements like maintaining posture. They do not fatigue so easily,
c intermediate fibres are in between fast and slow fibres. They do not fatigue as easily as fast fibres (like posture-maintaining muscles).
5
Muscle contraction is either:
a isometric, where the length of muscles does not change,
b isotonic, where the tone in muscles does not change but the length changes (as in movements).
6
Muscles consume a huge amount of energy when contracting and therefore have to generate their own energy molecules. These are produced by:
a aerobic methods in slow fibres, as oxygen is readily available from blood and myoglobin
b anaerobic methods in fast fibres where energy molecules are produced by incomplete combustion of glucose without using oxygen. This latter method produces more lactic acid, which is the origin of muscle fatigue.
7
Muscles contract because of stimulation by motor nerves of the fibres, which in turn, through a complex biochemical reaction in the presence of calcium, produce a sliding of specialised protein fibres into each other, causing contraction. Thus muscles have neurological as well as physical aspects of their function. They conduct electrical impulses as well as generate tension or power through actual physical movement.
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